12-11-2012, 05:57 PM
Adaptive modulation for space–frequency block coded OFDMsystems
Adaptive modulation.ppt (Size: 853 KB / Downloads: 29)
Abstract
The growing popularity of orthogonal frequency division multiplexing(OFDM) systems has created the need for adaptive modulation to integrate temporal, spatial and spectral components together
Then a new scheme consisting of a combination of adaptive modulation, OFDM, high-order space-frequency block codes (SFBC), and antenna selection is presented
To provide high-quality transmission for broadband wireless communications
Improve the performance of the SFBC–OFDM systems
INTRODUCTION
The adaptive Modulation is to improve the operational efficiency of Microwave links by increasing network capacity over the existing infrastructure
Conventional fixed-mode modulation schemes suffer from errors caused by deep fades
Adaptive scheme based on a set of mode switching levels designed for achieving a high average bits per second (BPS) throughput,while keeping the target BER of the system at a desired level
Adaptive modulation provides promising advantages compared to the fixed-mode schemes in terms of BER performance, spectral efficiency
AOFDM based on mode switching levels
In this case, we determine the switching level, which is the lowest required SNR for a given mode corresponding to a given target BER
we select the modulation mode.
This provides the largest throughput while maintaining the target BER
CONCLUSION
In this article, a new scheme of adaptive modulation for SFBC–OFDM aided antenna selection is presented
The spectral efficiency advantage of the proposed system is examined
It is shown that antenna selection with adaptive modulation can greatly improve the performance of conventional SFBC–OFDM systems
From a practical point of view, the effects of channel estimation errors and feedback delay on the overall performance of the presented system is currently under investigation